One problem encountered when handling small fluid sample volumes in devices is the non-specific adsorption of the sample on surfaces of the device. The term sample as used herein is defined as any fluid comprising a material that is the subject of an analysis. In some cases, the sample comprises a material dissolved or suspended in a liquid. In other cases, the sample comprises liquid, or mixture of liquids, that is itself the material subject to analysis. Sample adsorption can be problematic in analytical devices that transport and analyze small volumes. Substantial amounts of sample, sometimes the entire sample, can adhere to a surface of the device while being transported to a particular location in the device designated for analysis. This is especially problematic when handling biological samples comprising materials such as proteins or DNA, although similar concerns exist for the analysis of non-biological samples. In other cases the fluid in which the material of interest is dissolved or suspended can adhere to device surfaces, thereby undesirably altering the concentration of material in the sample.
Undesired sample adsorption can substantially reduce the amount of sample delivered to the analytical site of the device, thereby reducing the sensitivity of the analysis. Moreover, if the sample later de-adsorbs from device surfaces it can then become a contaminant in subsequent analyses, causing a reduction in the accuracy of the analysis. Additionally, the adsorbed sample can interact with subsequent samples, thus further altering the concentration or composition of the subsequent sample and therefore reducing the sensitivity or accuracy of the analysis.
Embodiments of the present invention overcome these problems by providing a device that reduces the non-specific adsorption of sample on a surface of the device, as well as by providing methods of using and making such a device.